This invention relates to the bottom-hole coring of subsurface formations. Samples of earth material are taken from subsurface formations for various purposes. For example, samples are taken to obtain information concerning the chemical or physical characteristics of an earth material, such as permeability, porosity or fluid saturation. In the exploration for and production of oil and gas, samples of earth materials are taken ordinarily by means of a core drill and the samples obtained are in the form of cylinders or cores. Drilling muds with a water or oil base are commonly used as coring fluids. These drilling muds are normally formulated to provide desired density and rheological properties which make them particularly suitable for use in coring wells.
Slim hole drilling is receiving considerable attention as a method of reducing drilling costs in remote areas. It also has the advantage that a continuous core is retrieved. Such slim hole drilling is adequately described in (i) "Slim Hole Drilling--Conclusion" by K. B. Gunn, Oil & Gas Journal, May 13, 1991, pgs. 51-55, (ii) "Slimhole Continuous Coring and Drilling in Tertiary Sediments" by S. B. Randolph and A. P. Jourdan, SDE/IADC Drilling Conference, Amsterdam, Mar. 11-14, 1991, paper no. 21906, (iii) "Mining Technique Finds Applications in Oil Exploration" by E. P. Deliac, J. P. Messines and B. A. Thierree, Oil & Gas Journal, May 6, 1991, pages 85-90, and (iv) "An Innovative Approach To Exploration and Exploitation Drilling: The Slim-Hole High-Speed Drilling System" by S. H. Walker and K. K. Millhelm, Journal of Petroleum Technology, September 1990, pages 1184-1191.
The continuous coring system described in these articles allows recovery of the inner tube of the core barrel by using a wireline and without tripping the drillstring. The retrieved core sample is typically pumped out of the core barrel into a trough where it is cleaned, marked and geologically described. The core sample may then be subjected to on-site physical testing, such as the measurement of core gamma or core spectral gamma by a conventional gamma ray logging system, and then repackaged for shipment.
It is an object of the present invention to provide both a method and apparatus for more efficiently handling a slim hole drilled core sample so that the cost advantage of the slim hole drilling is not eliminated by the high cost of evaluating the core material once it is retrieved to the surface of the earth.